In the description of the background of the present invention that follows reference is made to certain structures and methods, however, such references should not necessarily be construed as an admission that these structures and methods qualify as prior art under the applicable statutory provisions.
It is often desirable to separate a bearing ring into different pieces by intentionally fracturing the ring at a desired location.
One such bearing ring that is advantageously fractured at one or more locations along its circumference is an outer ring of a spherical plain bearing. Spherical plain bearings are used in numerous applications, such as in construction and other equipment.
FIG. 1A is a plan view of a spherical plain bearing 200. The bearing 200 generally comprises a continuous inner ring member 202 and an outer ring member 204. The outer ring 204 as illustrated in FIG. 1A is "double fractured" or segmented into two pieces that can be moved apart and mounted over the inner bearing ring 202. When mounting of the outer ring 204 is complete, the free ends 205 of the double fractured ring are brought together and the gaps between the two ring parts are closed.
FIG. 1B is a cross-sectional view taken along the section line 1B--1B of FIG. 1A, and illustrates certain features of the inner bearing ring 202. The inner bearing ring 202 generally includes a substantially cylindrical inner surface 206, and optionally having an inner peripheral groove 208 which distributes lubricant along the inner surface 206, the edge surface 210 and the outer arcuate surface 212 of the inner bearing ring 202. The outer arcuate surface 212 of the inner bearing ring 202 may optionally be provided with an outer peripheral groove 213 disposed therein. A through hole (not shown) radially interconnecting the inner and outer peripheral grooves 208 and 213 may also be provided for allowing lubricant to flow between the grooves 208 and 213.
FIG. 1C is a sectional partial perspective view of the outer bearing ring 204, prior to fracture. The outer bearing ring 204 generally comprises an inner arcuate surface 214 that receives the outer arcuate surface 212 of the inner bearing ring 202 in a nested relationship. The edge surfaces 216 of the outer bearing ring 204 each extend radially, and are interconnected by a substantially cylindrical outer peripheral surface 218. An outer peripheral groove 220 may be provided in the outer peripheral surface 218 of the outer bearing ring 204 to distribute lubricant along the outer peripheral surface 218.
A notched area 222 is provided in the outer bearing ring 204 by any suitable material removal technique, such as sawing or milling. The notched area 222 does not extend completely through the bearing ring 204. A centrally-located blind hole 224 or a multiple number of blind holes across the surface 218 may also be provided in the outer bearing ring 204. The blind hole 224 may be formed by any suitable material removal technique, such as drilling. Although only one notched region 222 and accompanying blind hole 224 are shown in FIG. 1C, typically a substantially identical construction is provided on the diametrically opposite side of the outer bearing ring 204.
FIG. 1D is a cross-sectional view taken along the section line 1D--1D of FIG. 1C and illustrates certain features of the notched area 222. A gap or space 226 on either side of the cross-section of the outer ring 204 represents the area where the material of the outer ring 204 has been removed to form the notched area 222. As illustrated by gap 226 in FIG. 1D, only a portion on either side of the cross-section of outer ring 204 is removed. That portion of the cross-section that remains defines an interconnecting region or fracture region 228 which is represented by the cross-hatched area shown in FIG. 1D. The interconnecting region 228 is bounded by the inner arcuate surface 214, a portion of the edge surfaces 216, the arcuate surfaces 230 on either side of the cross section, and a portion of outer substantially cylindrical surface 218. The blind hole 224 may be provided in the region 228.
The outer ring 204 with the above-described construction is case or surface hardened and then fractured. The outer ring 204 is fractured along the interconnecting region 228 to form two ring parts having separated ends 205 (FIG. 1A). The outer ring 204 is fractured by the application of mechanical force to the outer periphery of the ring in the notched area(s) 222.
By providing the interconnecting region 228 with a relatively small cross-sectional area the case hardening or surface hardening treatment can more easily penetrate through the entire interconnecting region 228 and cause this region to become sufficiently "brittle", thus facilitating fracturing. In addition, the blind hole 224 is provided to further facilitate the penetration of the case or surface hardening treatment through the cross section.
The fracture mechanics of this construction can be better understood by reference to FIGS. 1E-1H. Typically, a pair of notches N1, N2 is formed at both axial sides of the ring 204. As a mechanical force MF is applied to the outer periphery of the ring 204, cracks A, B originate within the interconnecting region 228 at points IE A.sub.o, B.sub.o in the vicinity of the notches N1, N2, respectively. These cracks A, B propagate toward each other.
Under ideal circumstances, cracks A, B propagate toward each other until the leading end or tip of one crack A, B runs into the leading end or tip of the other crack B to thereby define a fracture plane F corresponding to a line interconnecting B.sub.o, B and A.sub.o, A, as illustrated in FIG. 1F. However, it has been discovered that in practice this rarely occurs. Instead, a fracture pattern similar to that illustrated in FIG. 1G and/or FIG. 1H often occurs.
As shown in FIG. 1G, the cracks A, B propagate toward one another, but the leading ends or tips of the cracks pass one another and do not intersect. Instead, the leading end of one crack B may eventually run into or intersect a portion of the other crack A at a point spaced from the leading end of the other crack A. The distance between this point of intersection and the leading end of the crack being intersected A defines a secondary fracture SF which represents a residual fracture or crack that is not needed to form the fracture plane across the cross section of the outer ring 204.
Alternatively, as shown in FIG. 1H, the leading end of one crack may never entirely intersect the body of the other crack. Instead, an offset crack OC can form between the leading end of one crack B, with this offset crack C then intersecting the body of the other crack A. This forms a secondary fracture SF between the point where offset crack OC intersects the body of the crack A and the leading end of the crack being intersected A.
These secondary or residual fractures define a weakness in the cross-section of the outer ring 204 and can further propagate, possibly causing a chip of material to be dislodged from the outer ring 204. This can result in a reduction in service life of the bearing and the equipment in which the bearing is installed.
After the outer ring 204 has been fractured at the region 228, the resulting free ends 205 have a surface area defined by the area of the region 228. The free ends 205 are brought into contact with each other after the outer ring has been placed over the inner ring 202. Because the area of the region 228 is relatively small, by virtue of the amount a significant amount of material removed from the cross section in the regions 226, the contact pressure between the free ends 205 of the split ring is relatively large. This increased contact pressure can cause damage to the ends 205 of the outer ring 204.
Therefore, it would be desirable to provide a notched area that promotes cleaner separation by reducing or eliminating secondary fractures.
It would also be advantageous to reduce the amount of material removed from the cross-section when forming the notched area in order to maintain a relatively large area of contact between the free ends formed by the fracture, thereby reducing the contact pressure between the free ends of the outer ring. In addition, it would be advantageous to reduce the amount of machining or milling required to remove material from the cross section when forming the notch area.